阅读说明：本技术 一种聚偏二氟乙烯改性的锰酸锂正极材料及其制备方法 (Polyvinylidene fluoride modified lithium manganate positive electrode material and preparation method thereof ) 是由 白玉俊 慕春霖 亓永新 于 2021-06-28 设计创作，主要内容包括：本发明提供了一种聚偏二氟乙烯改性的锰酸锂正极材料及其制备方法。包括如下步骤：按质量比称取聚偏二氟乙烯和锰酸锂,加入去离子中水搅拌均匀后,转移到有聚四氟乙烯内衬的不锈钢水热反应釜中,加热到170-200℃并保温8-12小时,冷却后在107℃烘箱内烘干产物。本发明制备的聚偏二氟乙烯水热改性锰酸锂正极材料,具有优异的离子传导性能,作为锂离子电池正极材料,具有较高的倍率性能和良好的循环稳定性。(The invention provides a polyvinylidene fluoride modified lithium manganate positive electrode material and a preparation method thereof. The method comprises the following steps: weighing polyvinylidene fluoride and lithium manganate according to the mass ratio, adding deionized neutral water, uniformly stirring, transferring to a stainless steel hydrothermal reaction kettle with a polytetrafluoroethylene lining, heating to 170-200 ℃, preserving heat for 8-12 hours, cooling, and drying the product in a drying oven at 107 ℃. The polyvinylidene fluoride hydrothermal modified lithium manganate positive electrode material prepared by the invention has excellent ion conduction performance, and has higher rate performance and good cycle stability when being used as a lithium ion battery positive electrode material.)

1. The polyvinylidene fluoride modified lithium manganate cathode material is characterized in that the cathode material is a polyvinylidene fluoride coated lithium manganate material, and fluorine is doped into lithium manganate.

2. The polyvinylidene fluoride-modified lithium manganate positive electrode material as set forth in claim 1, wherein said lithium manganate has a polyvinylidene fluoride coating layer on its surface, and said coating layer has a thickness of 5 to 6 nm.

3. The polyvinylidene fluoride-modified lithium manganate positive electrode material according to claim 1, wherein said lithium manganate is a spinel-type lithium manganate.

4. The method for preparing a polyvinylidene fluoride-modified lithium manganate positive electrode material as set forth in any one of claims 1 to 3, characterized by comprising the steps of: uniformly mixing polyvinylidene fluoride and lithium manganate, and then carrying out hydrothermal reaction at the temperature of 170-200 ℃ to prepare the lithium manganate.

5. The method for preparing the polyvinylidene fluoride-modified lithium manganate positive electrode material as set forth in claim 4, wherein the mass ratio of the polyvinylidene fluoride to the lithium manganate is 0.3-2: 100, respectively; preferably, the ratio is 0.5-2: 100, respectively; further, the mass ratio of the polyvinylidene fluoride to the lithium manganate is 0.5:100 or 1:100 or 1.5: 100.

6. the method according to claim 4, wherein the polyvinylidene fluoride and lithium manganate are uniformly mixed in water, and the water is added so that the liquid surface exceeds the solid surface by more than 2.0 cm.

7. The preparation method of the polyvinylidene fluoride-modified lithium manganate cathode material as set forth in claim 4, wherein the hydrothermal reaction time is 6-15 h; preferably, the time is 8-12 h; further, 8h, 10h or 12 h.

8. The method for preparing the polyvinylidene fluoride-modified lithium manganate cathode material as described in claim 4, wherein said method further comprises the following steps: after the reaction kettle is cooled, drying a product to obtain the polyvinylidene fluoride modified lithium manganate cathode material; preferably, the drying of the product can be realized by an oven drying mode, the drying temperature is 100-110 ℃, further 105-107 ℃, and the specific examples are 105 ℃, 106 ℃ or 107 ℃.

9. A positive electrode of a lithium ion battery, which is characterized in that the positive electrode of the lithium ion battery comprises a positive electrode current collector, the surface of the current collector is coated with a positive electrode material, and the positive electrode material comprises the polyvinylidene fluoride modified lithium manganate positive electrode material of any one of claims 1 to 3.

10. A lithium ion battery, characterized in that the lithium ion battery comprises the polyvinylidene fluoride-modified lithium manganate positive electrode material of any one of claims 1 to 3 or the lithium ion battery positive electrode of claim 9.

Technical Field

The invention belongs to the technical field of lithium ion battery anode materials, and particularly relates to a polyvinylidene fluoride (PVDF) -modified lithium manganate anode material, a preparation method thereof, a lithium ion battery anode comprising the PVDF-modified lithium manganate anode material and a lithium ion battery.

Background

The information in this background section is only for enhancement of understanding of the general background of the invention and is not necessarily to be construed as an admission or any form of suggestion that this information forms the prior art that is already known to a person of ordinary skill in the art.

The lithium ion battery is green, environment-friendly and renewable energy storage equipment, and has been widely applied in various fields due to the unique advantages of the lithium ion battery. Lithium ion batteries with high energy density, long cycle life, lightweight design, and low cost have become the first choice for many energy storage devices. In lithium ion batteries, the choice of the positive electrode material is one of the key factors affecting the performance of the battery.

The lithium manganate cathode material has the advantages of low price, high potential, environmental friendliness, high safety performance and the like, and is hopeful to replace lithium cobaltate to become a new generation of lithium ion battery cathode material. However, during the charge-discharge cycle of lithium manganate, Mn is present³⁺The Jahn-Teller effect is generated to make LiMn₂O₄The spinel structure is converted into a tetragonal phase structure with poor stability, and meanwhile, the crystal lattice shrinks or expands to cause the crystal lattice to collapse and cause capacity attenuation, so that the lithium manganate anode has the problems of poor cycle performance, fast capacity attenuation, poor rate capability and the like in practical application, and the requirement of a rapidly developed energy storage technology is difficult to meet.

In order to improve the defects of poor cycle performance and rate performance of lithium manganate positive electrodes, some research works have been carried out, wherein surface coating and element doping are two commonly used methods. The surface coating can inhibit manganese element from being dissolved into electrolyte to a certain degree, but can not radically reduce Jahn-Teller distortion effect and can also reduce specific capacity. The modification effect of multi-element synergistic doping is generally better than that of single element doping, the cycle life of the battery can be prolonged, but bulk phase doping reduces the capacity decay rate at the expense of reducing the battery capacity. Therefore, other methods for improving the electrochemical performance of lithium manganate are explored, and the method has great significance for promoting the application of the lithium manganate cathode material in the lithium ion battery.

PVDF has been used in the prior art mainly as a binder for electrode materials, separator and polymer electrodesThe electrolyte can also be used to modify lithium metal electrodes. For example, patent No. CN201510756382.5 proposes a toughened and modified PVDF-based lithium battery separator and a method for preparing the same. In the reference (Advanced Energy Materials,2017,1701482), a high polarity β -PVDF is coated on the surface of lithium metal to suppress the formation of lithium dendrites and improve the electrochemical performance of the lithium metal battery. In the reference (Nano Letters,2021, DOI:10.1021/acs, Nanolett.1c01241), a porous lithium-philic polymer coating is formed by phase separation of PVDF-Polyacrylonitrile (PAN) blend, which can stabilize the lithium metal negative electrode, facilitate uniform deposition of Li and accelerate the Li deposition⁺And (4) diffusion. These techniques require PVDF to be dissolved in an organic solvent, i.e., dimethylacetamide or N-methylpyrrolidone, and then applied to the surface of lithium metal to modify the lithium metal, which is costly and has poor operability.

Disclosure of Invention

Aiming at the technical problems mentioned in the background technology, the invention provides a preparation technology of a polyvinylidene fluoride (PVDF) modified lithium manganate positive electrode material and application thereof in a lithium ion battery, and well solves the defects of the lithium manganate positive electrode material in the aspect of electrochemical performance.

Based on the technical effects, the invention provides the following technical scheme:

in a first aspect of the invention, a polyvinylidene fluoride (PVDF) -modified lithium manganate positive electrode material is provided, in the positive electrode material, a polyvinylidene fluoride covers a lithium manganate material, and fluorine is doped into lithium manganate.

The lithium ion battery anode material provided by the invention adopts lithium manganate as an anode material, the lithium manganate is recognized as one of more promising lithium ion anode materials in the field, has the advantages of rich resources, low cost, no pollution, good safety, good rate capability and the like, is an ideal power battery anode material, but the poor cycle performance and electrochemical stability greatly limit the industrialization.

PVDF is a non-reactive thermoplastic fluoropolymer of formula- (C)₂H₂F₂) n-, the melting point is 170 ℃, the thermal decomposition temperature is over 316 ℃, the long-term use temperature is-40-150 ℃, and the water-insoluble food has the characteristics of water solubilityGood chemical corrosion resistance, high temperature resistance, oxidation resistance, special performances such as pyroelectricity and the like. According to the positive electrode material provided by the invention, the PVDF is adopted to coat the lithium manganate material, the polyvinylidene fluoride forms a coating layer on the surface of the lithium manganate, firstly, the PVDF physically coating mode inhibits manganese elements from being dissolved into electrolyte, the Jahn-Teller effect is reduced, and the stability of the lithium manganate is improved. In addition, the lithium manganate has the defect of poor conductivity, and the conductivity of the lithium manganate is improved through fluorine doping. Compared with the mode of improving the stability of the lithium manganate by bulk phase doping in the prior art, the lithium manganate provided by the invention has the advantages that the crystalline phase structure of the lithium manganate is basically not changed, the battery capacity is reserved to a greater extent, and meanwhile, the stability of the anode material is improved.

In order to obtain the cathode material with the structure, the invention also provides a mode for preparing the lithium ion battery cathode material by a hydrothermal method. In the prior art, a technical scheme for forming a fluorine-doped carbon coating layer on the surface of an oxide negative electrode material by pyrolyzing PVDF at high temperature exists, however, the inventor finds that H is decomposed from PVDF by heating under the condition of high-temperature heating₂And reducing substances such as carbon and the like can reduce manganese elements in the lithium manganate into bivalent manganese, so that the charge and discharge activity is lost. According to the method, a hydrothermal method is adopted within the temperature ranges of the PVDF melting point being above 170 ℃ and below 200 ℃, the PVDF structure is not damaged, a modification layer can be formed on the surface of lithium manganate, fluorine doping is generated in the lithium manganate, the stability of the lithium manganate is improved, the electrochemical performance of the lithium manganate is improved, and a good modification effect is achieved.

Finally, the invention also provides the related application of the cathode material in the lithium ion battery.

The beneficial effects of one or more technical schemes are as follows:

according to the invention, by combining the performance characteristics of PVDF (polyvinylidene fluoride), the lithium manganate is subjected to modification treatment by a hydrothermal method, so that the stability of the lithium manganate anode material is improved, and the electrochemical performance of the lithium manganate anode material is improved:

1. the modifier PVDF has excellent chemical stability and thermal stability, high mechanical strength and no toxicity;

2. the PVDF modified lithium manganate positive electrode material is simple in preparation process, easy to operate and low in energy consumption;

3. the prepared PVDF modified lithium manganate positive electrode material has excellent ionic conductivity;

4. the prepared PVDF modified lithium manganate positive electrode material has high cycling stability and rate capability.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the invention and not to limit the invention.

FIG. 1 is an XRD (X-ray diffraction) pattern of a PVDF modified lithium manganate positive electrode material prepared in example 2;

FIG. 2 is an XPS plot of the original PVDF and PVDF modified lithium manganate positive electrode material of example 2;

FIG. 3 is a TEM image of the polyvinylidene fluoride-modified lithium manganate positive electrode material prepared in example 2;

FIG. 4 is a graph of rate capability and cycle performance at a current density of 100mA/g of the polyvinylidene fluoride-modified lithium manganate positive electrode material prepared in example 2 under different current densities.

Detailed Description

It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.

As introduced in the background art, lithium manganate as a positive electrode material has the defects of poor cycle performance and rate performance, and the prior art generally adopts a surface coating and element doping manner to improve the defects of lithium manganate, but cannot fundamentally solve the problems of distortion or capacity fading and the like of lithium manganate in the charging and discharging processes. The invention provides a polyvinylidene fluoride (PVDF) modified lithium manganate positive electrode material, which realizes the improvement of lithium manganate stability and electrochemical performance.

In a first aspect of the invention, a polyvinylidene fluoride (PVDF) -modified lithium manganate positive electrode material is provided, and the positive electrode material is a polyvinylidene fluoride-coated lithium manganate material, and fluorine is doped into lithium manganate.

In the cathode material provided by the invention, the surface of lithium manganate is provided with a polyvinylidene fluoride coating layer, and the thickness of the coating layer is preferably 5-6 nm.

It should be understood that references in the art to polyvinylidene fluoride, polyvinylidene fluoride resins, poly (vinylidene fluoride), polyvinylidene fluoride resins, and the like, all refer to the same material, polyvinylidene fluoride as described herein, having CAS number 24937-79-9.

The lithium manganate mainly comprises spinel lithium manganate and layered lithium manganate, wherein the spinel lithium manganate is stable in structure and easy to realize industrial production.

The second aspect of the present invention provides a preparation method of the polyvinylidene fluoride-modified lithium manganate positive electrode material of the first aspect, comprising the following steps: uniformly mixing polyvinylidene fluoride and lithium manganate, and then carrying out hydrothermal reaction at the temperature of 170-200 ℃ to prepare the lithium manganate.

Preferably, the mass ratio of the polyvinylidene fluoride to the lithium manganate is 0.3-2: 100, respectively; further, the ratio is 0.5-2: 100, respectively; in a specific embodiment, the mass ratio of the polyvinylidene fluoride to the lithium manganate is 0.5:100 or 1:100 or 1.5: 100.

preferably, the polyvinylidene fluoride and the lithium manganate are dissolved in water and uniformly mixed, and the water is added so that the liquid level exceeds the solid surface by more than 2.0 cm.

Preferably, the time of the hydrothermal reaction is 6-15 h; further, the time is 8-12 hours; in specific embodiments, 8h, 10h or 12 h.

The hydrothermal reaction is carried out in a hydrothermal reaction kettle, preferably a stainless steel hydrothermal reaction kettle with a polytetrafluoroethylene lining, the heating mode can be realized through an oven, and the uniformly mixed solution is transferred to the reaction kettle and is heated and kept warm in the oven.

Preferably, the preparation method further comprises a drying process of the product: and after the reaction kettle is cooled, drying the product to obtain the polyvinylidene fluoride modified lithium manganate cathode material. Further, the drying of the product can be realized by a heat drying mode such as an oven, and the drying temperature is 100-110 ℃, further 105-107 ℃, and the specific examples are 105 ℃, 106 ℃ or 107 ℃.

In a third aspect of the present invention, a lithium ion battery positive electrode is provided, where the lithium ion battery positive electrode includes a positive electrode current collector, a surface of the current collector is coated with a positive electrode material, and the positive electrode material includes the polyvinylidene fluoride (PVDF) -modified lithium manganate positive electrode material of the first aspect.

In a fourth aspect of the present invention, a lithium ion battery is provided, where the lithium ion battery includes the polyvinylidene fluoride (PVDF) -modified lithium manganate positive electrode material of the first aspect or the lithium ion battery positive electrode of the third aspect.

In order to make the technical solutions of the present invention more clearly understood by those skilled in the art, the technical solutions of the present invention will be described in detail below with reference to specific embodiments.

Example 1

0.015g of polyvinylidene fluoride and 3g of lithium manganate are weighed according to the mass ratio of 0.5:100, and are uniformly stirred in a beaker filled with 60ml of deionized water, and then are transferred to a stainless steel hydrothermal reaction kettle with a polytetrafluoroethylene lining. Heating to 200 ℃ in an oven, preserving the heat for 12 hours, and drying the product in the oven at 107 ℃ after cooling, namely the polyvinylidene fluoride modified lithium manganate positive electrode material.

Example 2

0.030g of polyvinylidene fluoride and 3g of lithium manganate are weighed according to the mass ratio of 1:100, and are uniformly stirred in a beaker filled with 60ml of deionized water, and then are transferred to a stainless steel hydrothermal reaction kettle with a polytetrafluoroethylene lining. Heating to 180 ℃ in an oven, preserving the heat for 12 hours, and drying the product in the oven at 107 ℃ after cooling, namely the polyvinylidene fluoride modified lithium manganate positive electrode material.

The XRD structure of the polyvinylidene fluoride hydrothermally modified lithium manganate positive electrode material prepared in this example is shown in fig. 1, and the modified lithium manganate spinel structure is not changed, but the insets show that the fluorine doping causes diffraction peak shift and the interplanar spacing becomes small.

The XPS structure of the polyvinylidene fluoride hydrothermally modified lithium manganate positive electrode material prepared in this example is shown in fig. 2, and compared with the original polyvinylidene fluoride (fig. 2 a), fluorine doping is realized in the modified lithium manganate (fig. 2 b).

A TEM image of the lithium manganate cathode material hydrothermally modified by polyvinylidene fluoride prepared in this example is shown in fig. 3, and a polyvinylidene fluoride modified layer is formed on the surface of the lithium manganate after the hydrothermally modification.

The performance of the half-cell assembled by the polyvinylidene fluoride hydrothermal modified lithium manganate positive electrode material and the lithium sheet prepared in this example is shown in fig. 4, and the half-cell is subjected to 10 charge-discharge cycles under the current densities of 20, 50, 100, 200, 400 and 800mA/g, and the average capacities are 128.1, 122.3, 113.3, 102.2, 87.0 and 64.6mAh/g (corresponding capacity retention rates are 100%, 95.5%, 88.4%, 79.8%, 67.9% and 50.4% respectively), which are significantly higher than the reversible capacities (118.9, 110.0, 100.7, 88.9, 73.1 and 53.2mAh/g respectively) and the corresponding capacity retention rates (100%, 92.5%, 84.7%, 74.8%, 61.5% and 44.7% respectively) of unmodified lithium manganate under the corresponding current densities. The cycling stability of the battery is also obviously improved compared with that of unmodified lithium manganate after the battery is subjected to charge-discharge cycling for 100 times under the current density of 100 mA/g. Therefore, the rate capability and the cycling stability of the lithium manganate cathode material are obviously improved by the hydrothermal modification of polyvinylidene fluoride.

Example 3

0.045g of polyvinylidene fluoride and 3g of lithium manganate are weighed according to the mass ratio of 1.5:100, are uniformly stirred in a beaker filled with 60ml of deionized water, and are transferred to a stainless steel hydrothermal reaction kettle with a polytetrafluoroethylene lining. Heating to 180 ℃ in an oven, preserving the heat for 12 hours, and drying the product in the oven at 107 ℃ after cooling, namely the polyvinylidene fluoride modified lithium manganate positive electrode material.

Example 4

0.015g of polyvinylidene fluoride and 3g of lithium manganate are weighed according to the mass ratio of 0.5:100, and are uniformly stirred in a beaker filled with 60ml of deionized water, and then are transferred to a stainless steel hydrothermal reaction kettle with a polytetrafluoroethylene lining. Heating to 180 ℃ in an oven, preserving the heat for 12 hours, and drying the product in the oven at 107 ℃ after cooling, namely the polyvinylidene fluoride modified lithium manganate positive electrode material.

Example 5

0.030g of polyvinylidene fluoride and 3g of lithium manganate are weighed according to the mass ratio of 1:100, and are uniformly stirred in a beaker filled with 60ml of deionized water, and then are transferred to a stainless steel hydrothermal reaction kettle with a polytetrafluoroethylene lining. Heating to 200 ℃ in an oven, preserving heat for 8 hours, cooling, and drying the product in the oven at 107 ℃, namely the polyvinylidene fluoride modified lithium manganate cathode material.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.